Muonium as a probe of electron spin polarisation in CdTe

Abstract: Muonium, consisting of a positive muon and an electron, is a pseudo-isotope of hydrogen. Muon spin rotation (mu SR) experiments with CdTe single crystals, nominally undoped, were performed at Paul Scherer Institut, in Switzerland, at 0.02 and 005 K and under an external transverse magnetic field up to 2T. A weakly bound muonium state is formed in CdTe with a very small hyperfine interaction (near 260 kHz). The frequency spectra show two muonium lines corresponding to different electron spin states (up and down) which have different energies in the presence of a magnetic field. The normalised intensity difference of muonium lines was used as a measure of the spin polarisation of the electrons captured by the muon. The electron spin polarisation in the muonium atom was found to be considerably lower than expected for a population in thermodynamical equilibrium; the data can be described by a modified Brillouin function with a saturation value which was found to change with the sample age. (C) 2009 Elsevier B.V. All rights reserved.